Elastic surfaces for sportsgrounds,playgrounds and footpaths



May 27, 1969 L. RAICHLE ETAL 3,446,122

ELASTIC SURFACES FOR SPORTSGROUNDS, PLAYGROUNDS AND FOOTPATHS I Filed Oct. 5, 1966 $heet of2 FIG I FIG. 4

INVENTORS LUDWIG RAICHLE BERNHARD WERMINGHAUSEN LEO UNBLERSTENHOEFER ATT'YS Maj 27, 1969 RAlcHLE ET AL 3,446,122

ELASTIC SURFACES FOR SPORT-SGROUNDS, PLAYGHOUNDS AND FOOTPATHS Filed Oct. 5, 1966 Sheet 3 of 2 FIG. 8

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LUDWIG RAICHLE BERNHARD WERMINGHAUSEN LEO UNT'ERSTENHOEFER ATT'YS United States Patent US. Cl. 94-7 11 Claims ABSTRACT OF THE DISCLOSURE A surface for recreational activities having a waterpermeable structure with a top cover layer, a bottom filter layer and an intermediate water-permeable elastic or highly resilient layer formed from particles of a closed-cell expanded plastic, e.g. homopolymers and copolymers of styrene or ethylene.

This invention relates to surfaces for sportsgrounds, playgrounds and footpaths having an elastic subbase.

Water-permeable, elastic surfaces are required for sportsgrounds and playgrounds and for footpaths and the like. They should allow rainwater to drain away and should lessen foot fatigue which occurs when walking or running on hard surfaces. A distinction is made between water-bound, mechanically stabilized surfaces and surfaces bound by bitumen, cement or plastics, the term surface referring to the whole construction of the sportsground, playground or footpath.

Water-bound surfaces are made up of materials having different particle sizes. They consist of different layers, for example in the case of a sportsground of a layer of red gravel, a layer of middle-grain cinders and a layer of broken brick or broken stone. A turfed playground, in which for example a layer of soil is applied to a layer of round gravel and cinders, is also water-bound. When the foundation soil is not permeable to water, drainage pipes are provided to drain away water which percola-tes through the surfaces. Water-bound surfaces cannot be regarded as elastic, although it is possible to achieve a certain resiliency for example by grading the particle size in laying the cinders. A layer of tan bark is often laid in the case of footpaths. This has the disadvantage however that it rots in a comparatively short time.

Surfaces bound by bitumen, cement or plastics may be elastic or inelastic, water-permeable or water-impermeable. The surfaces consist of various layers, for example in the case of an elastic water-permeable sportsground surface of a layer of rubber cuttings, cork granules and stone chippings which is bound with bitumen, and a layer of fine cinders and broken stone which is laid on the soil. A Water-impermeable elastic surface may consist for example of a layer of rubber cuttings, asphalt, fine sand and bitumen containing fibrous material. The top layer is laid on a base similar in construction to a pavement as used in conventional road construction.

It is an object of the invention to provide a surface structure for recreational activities such as a sportsground, playground, footpath or the like which is water-permeable throughout its several layers and has a relatively flexible top covering surface supported on an elastic layer which in turn is applied over a bottom filter layer such as gravel, sand or the like. Another object of the invention is to provide an elastic layer intermediate a bottom filter layer and at least one top covering layer such that the resulting structure is not only water-permeable but is also capable of holding or retaining water absorbed therein. These and other objects and advantages of the invention will become more apparent from the following detailed discolsure.

In accordance with the present invention, it has now been found that a highly improved surface for recreational activities is aciheved by a structure which includes a water-permeable flexible top covering layer, a bottom filter layer and an intermediate water-permeable elastic layer disposed as a subbase over the filter layer and formed from particles of a closed-cell expanded plastic.

All closed-cell plastics, i.e. foam plastics whose cells are substantially closed, are suitable in principle for the elastic layers. Expanded homopolymers and copolymers of styrene and of ethylene are particularly suitable. The plastics should be in the form of small particles, beads, cylindrical granules or lumps such as are obtained by mechanical comminution of blocks. The average diameter of the particles should advantageously be from 2 to 12 mm. Spherical particles may be used with particular advantage. These particles are obtained for example by expanding styrene polymers containing expanding agents.

In a particularly advantageous embodiment of the invention, the plastics particles forming the elastic subbase are bonded. The amount of binder should only be such that interstices remain between the bonded particles, i.e. the plastics particles and the binder form a coherent layer which is permeable to water. Binders which withstand the action of water and microorganisms for long periods are particularly suitable. Preferred binders are bitumen, rubber, polyisobutylene and copolymers of acrylic acid and vinyl chloride or vinylidene chloride, and they are advantageously used in the form of dispersions.

According to another advantageous embodiment of the invention the closed-cell plastics particles are incorporated in an open-cell expanded plastic. The expanded plastic may be based on urea-formaldehyde condensates, phenolformaldehyde condensates or polyurethanes. The expanded plastic should be open-celled to make it permeable to water and air. It is advantageous to use 30 to 50% by volume of closed-cell plastic and 70 to 50% by volume of open-cell expanded plastic.

The layers according to this invention are suitable in principle for all surfaces of sportsgrounds, playgrounds or footpaths. The elastic layers should advantageously be 3 to 15 cm. in thickness. They bring about elasticity in the covering layers resting thereon and also, in the case of open-pored covering layers, aeration of the soil. Since the plastics repel water, percolation of water through the layer is ensured. The heat insulation provided by the expanded plastic, which prevents rapid penetration of cold into the foundation soil, so that expensive frost precautions are unnecessary, is a particular advantage. Footpaths and sportsgrounds whose covering layer is formed by a lawn are advantageously provided with a subbase of plastics particles and an expanded urea-formaldehyde condensate. It has been found that the grass ro ts grow from the humus layer into the open pored urea resin layer and embrace the elastic, expanded plastics particles. A particularly elastic sportsground surface is thus obtained which does not lose its elasticity even after a long time. These surfaces also have the advantage that rapid drying out of the turf is prevented because the open-pored expanded urea resin absorbs water and only gives it up slowly to its surroundings. It has been found that grounds having other covering layers, such as tennis courts, when elastic subbases of plastics particles and expanded urea reins are used, taken longer to dry out than surfaces of tennis courts of conventional construction.

The load carrying capacity and elasticity of the elastic subbase may be adjusted in a desired manner by choice of the raw materials and by the construction of the granular subgrade.

Those surfaces are particularly advantageous which have a water-permeable covering layer of broken stone or stone chippings which is bound with mixtures of bitumen and plastics. Such covering layers are flexible and adapt themselves particularly well to the movement of the elastic subbase.

Another embodiment of the invention consists in arranging the surface consisting of the various layers in a trough consisting of a water-impermeable material, for example hard rubber or polyethylene. The trough should be connected by at least one pipe with means for regulating the level of water in the filter layer and elastic subbase up to the covering layer so that by evaporation of the water a continual soaking of the covering layer is provided. This embodiment has proved to be suitable for example for tennis courts.

Advantageous embodiments of the invention are illustrated in the following examples and the accompanying drawings.

EXAMPLE 1 FIGURE 1 illustrates an embodiment of an elastic surface construction which is eminently suitable for childrens playgrounds and the like. A dispersion-bound water-permeable rigid foam layer 2 having a thickness of 4 cm. is applied to a filter layer 1 of gravel or sand which has been compacted by rolling or vibration and which has a thickness of 10 to 15 cm. depending on the subgrade. The layer 2 consists of spherical particles of expanded polystyrene having a diameter of 2 to 10 mm. and a bulk density of 18 g./ 1. The particles are bound together with a waterproof polymer dispersion based on polyisobutylene. 10 to 15 liters of a 50% dispersion is used per cubic metre of expanded polystyrene particles. The plastics subbase 2 consists of prefabricated sheets. A water-bound covering layer 3, 3 to 4 cm. thick, is applied and compacted in the usual way.

The rigid foam layer imparts high elasticity to the surface so that the seriousness of injuries brought about by falls is diminished.

EXAMPLE 2 Another embodiment of elastic surfaces is shown in FIGURE 2. This is particularly suitable for running tracks, runways, tennis courts and the like. The thickness of the compacted filter layer 1 is 10 to 15 cm. The water-permeable plastics subbase 2 placed above the filter layer and having a thickness of 5 cm. consists of particles of expanded polyethylene in spherical form having a diameter of 2 to mm. and a bulk density of 30 g./ l. The particles of rigid foam are bonded with a 40% dispersion of an acrylic ester copolymer, an amount of liters per cubic meter of the rigid foam particles being used.

The rigid foam and the dispersion are mixed on the job site with a simple forced circulation mixer (concrete mixer), applied immediately to the filter layer 1 and compacted by light pressure. There are then applied to the set subbase 2 cinders 3 and a waterbound covering layer 4 having a thickness of 3 cm. and these are compacted. The layer of cinders 3 ensures favourable load distribution, good interlocking of the surface 4 and the subbase 2, particularly against shear stresses, and a slight decrease in the elasticity. These properties are specified for surfaces subjected to stresses such as occur during running with studded or spiked shoes and .in jumping events.

EXAMPLE 3 A embodiment of an elastic surface having good permeability to water is illustrated in FIGURE 3. A compacted filter layer 1 about 10 to 15 cm. in thickness has applied to it an elastic subbase 2 which is prepared from a rubber dispersion as a binder and a closed-cell rigid foam based on polyurethane which is in the form of lumps having a diameter of 5 to 12 mm. 15 to liters of the 30% dispersion is used for each cubic meter of expanded plastics particles.

4 The two components (expanded plastic and dispersion) are mixed in a continuous mixer and applied in the desired thickness. After the 2-crn. elastic subbase 2 has set, a 4-cm. course of cold asphalt 5 is laid thereon and compacted, the grain size of the stone chippings being mainly from 3 to 8 mm. to provide water-permeability. The bituminous binder component is 5 to 6% on the whole composition.

The water-permeable elastic subbase 2- imparts high elasticity to the surface, so that such surfaces are particularly suitable for playgrounds.

EXAMPLE 4 The filter layer 1 shown in FIGURE 4 is equivalent to that in FIGURES 1 to 3. A mixture of spherical expanded polystyrene particles having a diameter of 2 to 10 mm. and an open-pored expanded plastic of a urea-formaldehyde condensate is used for the elastic subbase. The two components are mixed in the ratio by volume 50:50 in a continuous machine, and then sprayed onto the filter layer 1 and lightly compacted with a rammer. The covering layer 6 is a permeable water-bound surface which is applied and compacted after the plastics subbase 2 has hardened.

The subbase 2 having a thickness of 8 cm. imparts not only high elasticity but also a certain water-retaining property, yet water permeability of the material is ensured. The water retained in the expanded plastic is given up to the covering layer when the ambient temperature is high and hinders rapid drying out of the same with the formation of dust.

These surfaces are particularly suitable for footpaths.

EXAMPLE 5 Another elastic surface construction is illustrated in FIGURE 5. The filter layer 1 is constructed according to the foundation soil, analogously to the preceding examples. The water-permeable and elastic subbase 2 which is 10 cm. in thickness is made of spherical expanded polystyrene particles with a diameter of 2 to 10 mm. and a dispersion of a vinyl chloride copolymer. 15 liters of the 40% dispersion is used for each cubic meter of expanded plastics particles. Mixing is carried out with a simple forced circulation mixer. The material is then spread out and lightly compacted.

After it has set, a layer 7 having a thickness of 1 to 3 cm. is built up from stone chippings having a particle size of 38 mm. A water-permeable covering layer 8 is applied to this coating by the hot-laid method. The coating consists of stone chippings having a particle size of 012 mm. and a binder of 70 parts of bitumen having a penetration of according to DIN 1995 and 30 parts of a copolymer having a melt index of 3.5 from 82 parts of ethylene and 18 parts of n-butyl acrylate. The content of binder is 9% on the whole mixture.

The mixture is prepared in a conventional mastic cooker. The material is poured at 180 to 200C. For this reason, layer 7 of stone chippings has to be provided to act as a heat shield, the rigid foam being resistant only to temperatures up to about C.

As a result of the binder of bitumen and plastic used an elastic asphalt coating is obtained having particularly favourable flexural properties. It is not effected by even marked movements of the elastic plastics subbase even at extreme temperatures. Crack formation, such as occurs with conventional bituminous coatings, particularly at low temperatures, does not occur in the coating described in this example.

Such elastic surfaces which are permeable to water owing to favourable gradation of particle size can be played on all the year round. They are suitable for playgrounds, pathways and the like.

EXAMPLE 6 A filter layer of round gravel and cinders in the ratio 1:1 having a thickness of 10 to 15 cm. (see FIGURE 6) has applied to it an elastic subbase 2 consisting of 30 parts of closed-cell polystyrene in the form of small pieces having diameter of 2 to mm. and 70 parts of an open-pored expanded plastic from a urea-formaldehyde condensate. Mixing of the components is carried out in a continuous machine. The mixture is sprayed onto the filter layer 1 and lightly tamped. The thickness of the layer 2 is '8 cm. The previously removed topsoil 9 is replaced in a thickness of about 10 cm. and seeded.

The expanded plastics subbase ensures good elasticity of the turf and prevents excessive consolidation. In addition, the water accumulated in the 70 parts of openpored expanded plastic prevents the turf from drying out, even if not watered for a long period. Moreover, good aeration of the top soil is ensured. As the grass roots grow into the open-pored expanded plastic, good interlocking of the elastic subbase and the topsoil is obtained.

EXAMPLE 7 FIGURE 7 shows the design of an elastic surface which is embedded in a trough so that it is possible to very at will the moisture content of the surface.

The excavation of a trough having the size of the playing field to be built is carried out so that there is a slight slope to the lowest point in one corner of the trough. The entire trough is sealed with a sheet 10 of polyisobutylene.

A layer 11, 2 cm. in thickness, of water-permeable dispersion-bound rigid foam is placed in the lined trough; this consists of expanded polystyrene particles having a diameter of 2 to 10 mm. and of isobutylene, liters of a 50% dispersion being used per cubic meter of expanded plastics particles for the preparation of the layer. A gravel filter layer 12, 10 to 15 cm. in thickness, is laid on the layer 11. To this there is then applied a waterpermeable dispersion-bound rigid foam layer 13 having the same composition as the layer 11. Then follows a layer 14 of cinders having a thickness of 2 to 3 cm. and finally a water-bound surface layer 15. Concrete tiles 16 are placed at the edges of the trough to serve as the boundary for the upper layers.

At the lowest point of the trough, the sealing foil is penetrated by an outlet pipe 17 consisting of a ground drain 18 and overflows 19, 20 and 21 at different levels and capable of being closed by caps. Depending on which of the three overflows is open, three different water levels may be set up in the trough. The overflow 21 is left open always to prevent flooding of the ground and serves at the same time as an inlet for filling the trough. Water coming from the overflows and ground drain runs away through a drainage pipe 22. The overflows and ground drain are covered by a tile 23.

This design makes it possible to keep the upper surface moist, cool and free from dust. Since it is possible to set up practically any elasticity of the surface by varying the thickness of the expanded plastic and cinder layers, such constructions are suitable particularly for tennis courts.

EXAMPLE 8 Another embodiment of an FIGURE 8. Trenches 25 subgrade 24. A sheet 26 based on polyisobutylene and having a thickness a 4 mm. is laid on the subgrade thus prepared. Drainage pipes 27 are laid in the trenches 25. An elastic plastics layer 2 of particulate polystyrene and a polyisobutylene dispersion is then applied thereto. The upper-most layer 4 is a water-bound covering applied to the plastics layer 2.

Such a construction is particularly suitable for tennis courts.

We claim:

1. A surface for recreational activities comprising a water-permeable flexible top covering layer, a bottom filter layer and an intermediate water-permeable elastic layer disposed as a subbase over said filter layer and formed from particles of a closed-cell expanded plastic.

2. A surface as claimed in claim 1 wherein said particles of a closed-cell expanded plastic are loosely bound with an adherent binder applied from an aqueous dispersion such that interstices remain between the bonded particles to provide a coherent water-permeable elastic layer.

3. A surface as claimed in claim 2 wherein the binder is polyisobutylene.

4. A surface as claimed in claim 2 wherein the binder is rubber.

5. A surface as claimed in claim 2 wherein said binder is a copolymer of acrylic acid, vinyl chloride or vinylidene chloride.

6. A surface as claimed in claim 1 wherein said particles of a closed-cell expanded plastic are embedded in an open-celled expanded plastic to provide a coherent waterpermeable elastic layer.

7. A surface as claimed in claim 6 wherein said opencelled expanded plastic is a urea-formaldehyde condensate.

8. A surface as claimed in claim 1 wherein said closedcell expanded plastic is a substance selected from the group consisting of homopolymers and copolymers of styrene and ethylene.

9. A surface as claimed in claim 8 wherein said particles of a closed-cell expanded plastic have an average diameter of about 2 to 12 mm.

10. A surface as claimed in claim 9 wherein said particles of a closed-cell expanded plastic are embedded in an open-celled expanded plastic to provide a coherent water-permeable elastic layer.

11. A surface as claimed in claim 10 wherein the opencelled expanded plastic is a urea-formaldehyde condensate and said elastic layer consists essentially of 30 to 50% by volume of the closed-cell expanded plastic and to 50% by volume of the open-celled expanded plastic.

References Cited UNITED STATES PATENTS 2,067,356 1/1937 Swinhoe 94-7 X 2,225,458 12/1940 Murphy 947 2,837,984 6/1958 -Klozt 947 3,250,188 5/1966 Leonards 947 3,279,334 10/ 1966 Quartararo 94-4 X NILE C. BYERS, 111., Primary Examiner. 

